Battery Disconnect Switch

[TomInCologne]

Originally Posted by Phil Brown

All valid points for switching the ground side, no argument but why is it that all of the other electric components are switched on the non-ground side ? Headlights, cowl lights, dash lights even generator cut out

Because you don't want the switch for the headlights to be next to the headlights. You want the switch to be on your steering wheel. Think about it...

[WHN]

Originally Posted by Phil Brown

All valid points for switching the ground side, no argument but why is it that all of the other electric components are switched on the non-ground side ? Headlights, cowl lights, dash lights even generator cut out

As in your homes electrical lines, your wall switches switch the hot (black) wire. If you just were to switch the (white) wire neutral, you could still get a shock or sparks when working on the circuit. Switching black wire stops current from flowing to device. Lamp, toaster, iron, whatever.

In a two wire home wiring system, not todays code, the neutral wire is also the ground. Todays systems use three wires, hot black, neutral white, and ground bare.

To confuse all this as far as your home goes. You can under the right conditions get one hell of a shock off the white neutral wire. Feed back.

Turning off your circuit breaker, just switches off the black (hot) side of the circuit. The neutral and ground are still connected.

Use a double pole switch if you want to switch both the hot and neutral.

Cars only need one wire going to item to be powered, the hot. The rest of your car is grounded, no need for second wire. Your wooden house is not the same.

The affects of Electricity are the same whether AC or DC. You need a path to ground.

Did I confuse you.

[The Master Cylinder]

Originally Posted by Phil Brown

All valid points for switching the ground side, no argument but why is it that all of the other electric components are switched on the non-ground side ? Headlights, cowl lights, dash lights even generator cut out

Not all, what about the horn and ignition. The other circuits you mentioned you have to run two wires to in order to switch the ground side.

Originally Posted by WHN

As in your homes electrical lines,

Did I confuse you.

I stopped reading when you mentioned house wiring because houses are wired completely different and do not apply to the Model A..

[old31]

So the issue of not being able to turn off a running car with a alternator still exists, whether it be a negative or positive interrupt.

I just tried it on my car. I have an alternator and the kill switch is on ground. The car was running and and the kill switch could not turn the car off. DUH!

Does anyone have a fix for this?

[Y-Blockhead]

Originally Posted by old31

So the issue of not being able to turn off a running car with a alternator still exists, whether it be a negative or positive interrupt.

I just tried it on my car. I have an alternator and the kill switch is on ground. The car was running and and the kill switch could not turn the car off. DUH!

Does anyone have a fix for this?

We are talking disconnect switch not kill switch. Your ignition switch wouldn't turn it off either?

Same if you blow the fuse people install on the starter, Alternator continues to feed ignition.

You could have your wifey pull the coil wire??

I have a fuse in the ignition circuit so I guess I could pull that if I was ever in that situation.

I also have my ignition circuit wired so the ignition switch is before the coil.

[Phil Brown]

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Originally Posted by old31

So the issue of not being able to turn off a running car with a alternator still exists, whether it be a negative or positive interrupt.

I just tried it on my car. I have an alternator and the kill switch is on ground. The car was running and and the kill switch could not turn the car off. DUH!

Does anyone have a fix for this?

https://www.speedwaymotors.com/Speed...4aAgZeEALw_wcB

goes in the non-ground side

[johnneilson]

Originally Posted by old31

So the issue of not being able to turn off a running car with a alternator still exists, whether it be a negative or positive interrupt.

I just tried it on my car. I have an alternator and the kill switch is on ground. The car was running and and the kill switch could not turn the car off. DUH!

Does anyone have a fix for this?

Yes, this is a common problem while confusing a battery disconnect switch for kill switch. There are high amp disconnect switches with 2 NO contacts, one for battery and another for the ignition or charging system.
Adding a relay probably will not correct the issue.

J

[WHN]

Originally Posted by The Master Cylinder

Not all, what about the horn and ignition. The other circuits you mentioned you have to run two wires to in order to switch the ground side.



I stopped reading when you mentioned house wiring because houses are wired completely different and do not apply to the Model A..

I new that I had gone to far, but you missed the best part. That’s what happens when you get OLD.

Enjoy.

[01A]

If the positive battery terminal is considered 'hot' and the positive is connected to the chassis then the entire chassis is 'hot'. As an experiment disconnect the negative battery cable from the negative battery post, use a volt meter and connect the red positive lead to a clean chassis bolt and the black negative lead from the volt meter to the negative battery post and see if you measure 6 volts ( assuming a stock 6 volt positive ground) . what you have done is proved the cutoff switch on the negative battery post being in the off position does not keep the chassis from being hot (possibly including the motor ) so any short circuit from the hot chassis hitting the negative battery post would complete the circuit and sparks could fly. Thinking what could happen if a wrench dropped bridging the negative battery post and the frame/chassis.

[bbrocksr]

Originally Posted by Phil Brown

All valid points for switching the ground side, no argument but why is it that all of the other electric components are switched on the non-ground side ? Headlights, cowl lights, dash lights even generator cut out

Because they don't have a ground wire to put a switch in.
Bill

[bbrocksr]

Originally Posted by 01A

If the positive battery terminal is considered 'hot' and the positive is connected to the chassis then the entire chassis is 'hot'. As an experiment disconnect the negative battery cable from the negative battery post, use a volt meter and connect the red positive lead to a clean chassis bolt and the black negative lead from the volt meter to the negative battery post and see if you measure 6 volts ( assuming a stock 6 volt positive ground) . what you have done is proved the cutoff switch on the negative battery post being in the off position does not keep the chassis from being hot (possibly including the motor ) so any short circuit from the hot chassis hitting the negative battery post would complete the circuit and sparks could fly. Thinking what could happen if a wrench dropped bridging the negative battery post and the frame/chassis.

In a positive ground system the negative terminal is hot. The hot terminal is the ungrounded one.
Bill

[bbrocksr]

Originally Posted by Bob Bidonde

John Neilson, I agree with your position. It does not matter which battery cable the switch is in so long as it breaks the circuit when it is OFF.

If you break the ground the complete system is dead. Not so if you break the hot.
Bill

[old31]

y block, this is the switch that I am using. My ignition switch does turn the car off.

https://www.amazon.com/Current-Batte...xpY2s9dHJ1ZQ==

[johnneilson]

If you want the Main switch to kill the running engine you will need a switch with more than one circuit

Here is description from such a switch;

Master Battery Cutoff Switch with Alternator Protection
Click for a larger picture of Master Battery Cutoff Switch with Alternator Protection
This switch has three sets of contacts for cars with alternators. The main contacts disconnect the battery while the auxiliary contacts disconnect the ignition coil and short the alternator output to ground. A 3 ohm resistor (included) provides a load to protect the grounded alternator. A removable actuating key with splash guard, weather-proof cap, resistor and installation instructions are included.

[rfitzpatrick]

I have the switch on the plus side of my PicUp, it's near the starter. I have a 6 volt alternator, this set-up at least 4 years. I never been unable to shut down my engine using my shut-off. This being my experience, am I doing any harm to my electrical system?
TKS Guys

[duke36]

Originally Posted by bbrocksr

If you break the ground the complete system is dead. Not so if you break the hot.
Bill

Same experience

[Rob Doe]

You guys have me smiling. Just for fun, I'm gonna throw my hat inta the ring with yuns.

The BATTERY cutoff switch is only a battery cutoff switch. If the car's generator or alternator is putting out adequate voltage, meaning the engine is running, when you open your BATTERY cutoff switch, you'll need to turn the ignition key off to open the primary ignition circuit. Otherwise the alternator / generator will continue to feed the flames / juice to any circuit that is completed, by its switch being closed or by any short/s that complete a circuit back to the generator/alternator.

The battery is the voltage regulator for the stock Model A GENERATOR. I'm uncertain what failing to turn the ignition key off will do to your generator when you turn the BATTERY cutoff switch off but allow the engine to continue to run. I think the voltage will go thru the roof? I think you will see some smoke fairly quickly. Current does not flow if a circuit is not complete. For the alternator/generator to recognize/charge the battery, both battery posts must be connected. So, no matter what side the BATTERY cutoff switch is wired into, if the cutoff is open, the generator / alternator can't make use of the battery.

The reason the BATTERY cutoff is better placed in the ground side is that if the ground cable falls off the frame or the battery, no dangerous short can be created. Not so, if the cutoff is wired into the hot / negative cable. A frayed or broken negative cable flopping against the frame will absolutely create a zinger of a short. A short could occur inside the cutoff switch also.

I will wire my cutoff into the ground side. If the 1929 November wiring change has been applied to the car and accessories are sourced from the yellow/black stripe charge side of the ammeter, most shorts will show on the ammeter. However, a stuck closed starter switch will not. If the starter is stuck, I'll know it as soon as I take my foot off the button. In either case, time is of the essence. I want to reach between my legs and open all the battery circuits at once. I will then turn the ignition off if the engine is running.

ROTORWRENCH, where are ya, buddy.

[MilwaukeeMike]

They make a longer ground strap with additional holes. They really help.

[Phil Brown]

Originally Posted by MilwaukeeMike

They make a longer ground strap with additional holes. They really help.

Interesting, never seen one like that

[Russell Reay]

This has been quite a thread. In two years of reading this forum I recall several A owners having electrical problems which have been solved by improving connections in one place or another. The most annoying problem would be a poor connection/ short leading to a dead battery at a very inconvenient time. I installed a disconnect in the X-member close to that shown In #18. With size 0 and 00 cables, a cable connecting the transmission to the battery, gussets welded from the X-member to both frame rails, and the disconnect I think I have a bulletproof ground.